Structural and Optical Characteristics of Thin GaAs Films

Abstract

Structural, electrical, and optical measurements have been carried out on over 85 GaAs films deposited under high vacuum in a thickness range between a few hundred to 70 000 Å, and for substrate temperatures between 175° and 450°C. The films were textured when deposited above 220°C, exhibiting [110] textures below 280°C and [111] textures above 320°C. The films were always p type and the lowest resistivity measured was 20 Ω·cm. Films deposited below 280°C exhibit a fundamental absorption edge shift to lower energies; this shift is correlated with x‐ray line shift and annealing‐out measurements of conductivity. The absorption edge shift is attributed to a high concentration of vacancies trapped in the film during growth at low temperatures. An acceptor level 0.18 eV above the valence band is associated with these vacancies. The films exhibiting the anomalous shift can yield bulk optical properties by prolonged heating at 380°C. Films deposited above 320°C always exhibit properties characteristic of high‐resistivity bulk GaAs.